The invention relates to an apparatus and method useful for automatically tying bales of cotton or other fibers, and in particular, to an automatic bale tying apparatus for tying a plurality of plastic straps around a bale while reducing the stresses at the joint of the baling strap material.
In the cotton industry, the normal method of banding or tying cotton bales has been to have workmen direct a tie, such as a band or wire, around a bale and then secure the ends of the ties appropriately depending on the design of the tie. In the cotton or fiber industry, there are generally three ways in which to secure a bale after a bale has been pressed. Pertinent securing means include pre-formed steel wires that have interlocking ends pre-formed into loops which engage one another during the tying operation, flat ribbon-steel bands which have their ends inserted into a crimp by which they are secured, and flat thermoplastic strapping material, typically polyethylene or polyester.
Steel pre-formed wires have a loop manufactured into each end which are interlocked around a bale forming a square knot. When the pressure is released from the bale, the knot formed by the interlocking loops pulls tight and retains the bale against This paper or fee is being deposited with the further expansion. In a conventional bale-tying operation, two workmen (one on each side of the baling press) manually bend the wires around the bale and secure the ends of the wires together in a wire tie guide assembly. The wires are normally tied together sequentially, one at a time. Alternatively, wires might be tied in a hydraulically operated wire tying device for mounting on a baling press, which ties a plurality of wires having pre-formed interlocking ends around a bale formed in the press. Pivotally mounted wire bend assemblies take the place of workmen on each side of the baling press, and bend the tie wires around a bale by inserting the ends of the tie wires into a wire tie guide assembly. However, workmen are still required to individually load each of a plurality of tie wires into the wire bend assemblies.
Although an improvement over the manual-type bale tying operation, a hydraulically operated wire tying device still exhibits certain problems which slow the ginning process. Exact timing is required for the sequence of events which make up a wire tying operation. If a wire does not follow the correct path at the correct time, several factors can combine to prevent the interlocking ends of the wire from engaging in a knot. In particular, the interlocking ends of the wires are conventionally oriented such that the loops are disposed in the generally horizontal plane. This geometric orientation forces the wire closers to be constructed with relatively wide cavities, in order to accommodate the wide aspect ratios of the loops. This, in turn, allows the wires a greater degree of freedom of movement within the cavities. Consequently, there is a greater probability of one wire merely sliding past another, without their loops engaging in a knot.
In addition, press wear, both alone or in combination with component manufacturing tolerances, can cause a follow block to vary its position or orientation both vertically or from side to side. Consequently, the wire bend assemblies may not be in alignment with a wire tie guide assemblies. All the above-described cases result in mis-ties, with a consequent loss of time and possible damage to the press.
Bale tying using flat steel straps is hindered primarily by the cost of the strapping material, the complexity of the machinery used, and the speed at which the machinery is able to operate. In addition, the sheer weight of steel strap tie material and its substantially sharp edges, makes it cumbersome and particularly dangerous to handle. Further, once it is removed from a bale, steel strapping material is not easily recycled by an end user. Removal is difficult and, once removed, a large volume of sharp material must be colleted and crushed together to form it into a package that can be more easily handled. Notwithstanding the foregoing, steel strap tie material is further disadvantageous in that its weakest spot (the joint) is located in the highest stress position on the bale, because the forming machinery is only able to apply a joint (crimp) on the side of the bale, i.e. the bale position with the highest degree of lateral pressure or stress. This results in significant tie breakage with a consequent loss of bale integrity.
Conversely, plastic or non-ferrous strapping is an ideal material for strapping bales of cotton or other fibers. Plastic is relatively light in weight and can be formed into a variety of widths and thicknesses, and with soft edges, which allows easy handling and lowers shipping costs. Plastic or non-ferrous strapping material is very competitive with wire ties, on a cost per bale basis, and is easily adaptable to fully automatic tying machinery. Plastic or non-ferrous strapping material is readily recyclable by the end user and is considered substantially safer than steel strapping material, particularly in instances of strap breakage.
Because of the particular orientation of conventional plastic strap automatic tying machinery, certain disadvantages arise when one adapts strapping and joint forming apparatus to the structure of a baling press. Typically, automated thermoplastic strapping machinery, including a material feeder, tensioner, cutting shear and joint former, are so large that they are precluded from being able to be placed anywhere except on the side of the bale. As was the case with steel strapping material discussed above, thermoplastic strapping joint formation takes place in the region of the bale that exhibits the highest degree of tension stress.
In this regard, conventional thermoplastic strapping machinery must typically wait until a baling press has completed operation and has reached xe2x80x9cshut heightxe2x80x9d, before it begins the strapping operation. The strapping head pulls strapping material off of a spool and directs it around the bale through a series of shoots, until the front edge of the strapping material has completed its circuit of the bale and is directed back to the region of the strapping head. The strap is then pulled tight around the bale to a pre-determined tension and the strap is then cut with a shear. The two ends are then joined by a friction weld, hot knife weld, or other similar joint forming operation, and maintained together until the joint is cool, in which time the strap is released and allowed to carry the tension load of the bale.
Referring now to FIGS. 1a, 1b and 1c, there is shown a semi-schematic view of cotton, or other fibers, being pressed into a bale between the platens of a hydraulic press in accord with the prior art. Typically, fiber is pressed by a large hydraulic cylinder out of a box that measures approximately 30 inches wide by 54 inches long and 144 inches deep. Such a box is typically filled with approximately 500 pounds of cotton lint which is subsequently pressed into a 20 inch by 54 inch bale measuring approximately 20 to 22 inches tall (in accordance with the illustration of FIG. 1a). The box from which the bale is pressed has been omitted for the sake of illustrational clarity.
Strapping material, in the form of thermoplastic straps, are inserted through guide slots in the upper and lower platens, and are secured on the sides of the bale (as shown in the illustration of FIG. 1b). Once the bale is tied, the press is released and the bale is free to expand to the constraints of the straps. As shown in the illustrated embodiment of FIG. 1c, the bale is then dumped out of the press, making way for a subsequent box loaded with an additional 500 pounds of cotton lint for pressing into the next bale.
It should be noted that conventional thermoplastic strapping systems typically consist of three laterally spaced-apart strapping heads, such that the unit must be indexed in order to tie the requisite number of straps (typically 6) about a bale. Should the baling press leak down slightly (a typical artifact of cotton presses) the compressed bale would tend to grow as the press platens separated. When an indexing strapper is used, typically the #1, #3 and #5 straps are tied first. Five to ten seconds later, the strapping head is indexed and the #2, #4 and #6 straps are tied. In the event of press leakage, the first three straps are pulled tight around a smaller diameter bale. The second three straps are subsequently pulled tight around a bale that has expanded and are therefore not as tight. This causes the first three straps to be subject to substantially greater pressure than the second set. These ties are more prone to exceed yield strength and fail which typically causes total strap failure as pressure promptly increases for the ties of the second set.
Accordingly, an apparatus (and process) for tying bales with a flexible thermoplastic strapping material, that is designed for efficient, repeatable operation with low joint stress is needed. Such an apparatus should be designed for easy operation by a single workman to reduce labor costs, while at the same time being easy to install or retrofit to existing presses. Such an apparatus should further be mountable to operate in conjunction with a press such that ginning speed is increased by incorporating the tying process into the last few seconds of the bale pressing operation, thus eliminating the separate indexing and tying steps conventionally undertaken at the end of the process.
The present invention provides for an automatic bale strapping system which is permanently coupled to a baling press and which is loaded with a precut length of strapping material and which deploys for the tying operation while the press ram is still moving. In one aspect of the invention, first and second arm assemblies are pivotally mounted on opposite sides of the baling press and which receive and hold the entire length of a precut baling strap. The first and second arm assemblies pivot around a compressed bale as the assemblies rotate from a strap loading position to a welding position. At least one of the first and second arm assemblies include an extension means which protects an otherwise protruding end of the precut baling strap during the pivoting operation. The extension means subsequently retracts to thereby expose the end of the precut baling strap during the welding operation.
A movable follow block is mounted on the bale press ram and is forced against the bale by the press ram in order to compress the bale on the baling chamber. The follow block includes closure cavities which receive the first and second arm assemblies for welding engagement. A friction weld is formed in an interfacial region of overlapping strap ends with the subsequent weld being positioned in a region corresponding to the top or bottom surface of a bale formed in the press. The closure cavity comprises an elongated, open-ended cavity extending across the length of the follow block. The first arm assembly is inserted into a first end of a cavity as the first assembly is pivoted and the second arm assembly is inserted into a second, opposite end of the cavity, as the second assembly is pivoted.
In an additional aspect of the invention, a guide chute is disposed along each of the first and second arm assemblies which guides and retains a length of pre-cut bale strapping material. A feeder assembly is removably disposed at end of the first arm assembly and introduces a length of bale strapping material into the guide chutes of the arm assemblies. Feeder assembly includes a shear for cutting the strapping material to a predetermined length after the strapping is introduced into the device.
In a further aspect of the invention, each arm assembly includes a centrally disposed mounting plate which forms the surface of a baling chamber opposite the follow block. A pivotally movable arm is mounted on an outside edge of a mounting plate and is capable of being pivoted from a longitudinally extending loading position to a downwardly extending weld position. The finger assembly is mounted on the distal end of each arm with each finger assembly able to be pivoted with respect to the arm from a longitudinally extending loading position to a follow block insertion position. Each finger on the first arm assembly is associated with counterpart finger on the second arm assembly. The strapping device is constructed such that when both the arm and the fingers comprising the first and second arm assemblies are in their fully extended loading positions, each strap spans the baling press such that each end of the strap is collocated with an end of a respective finger assembly. The extension means comprises a strap tip protection sled which is slidably mounted on the outboard end of a corresponding finger assembly. The strap tip protection sled extends to cover the exposed strap tip during the pivoting operation and retracts to expose the strap tip during the welding operation. At least one of the finger assemblies includes guide means for guiding a first end of the strap into position in the finger assembly for welding and for guiding a received, opposite strap end into overlapping registration with the first end. The guide means includes a Chicane for bendably displacing the first strap end so as to form a stress relief bow.
In yet a further aspect of the invention, a level arm assembly is coupled between the central mounting plate and each finger assembly. The level arm assembly operates to control the angular position of each finger assembly with respect to the plane of the follow block. The level arm assembly guides each finger assembly into the closure cavity by adjusting the angular position of each finger assembly such that the finger assembly is level with respect to the plane of the follow block for easy insertion.
In summary, the bale strapping device ties thermoplastic straps around a bale which has been compressed into a generally rectangular form. First and second articulated strap tying assemblies are pivotally mounted on opposite sides of a central mounting member of a baling press. The first and second strap tying assemblies are disposed in mirror image fashion and in opposition to each other and are disposed to receive and hold the entire length of a baling strap which has been precut to a predetermined length. First and second finger assemblies are each disposed at a distal end of a respective first and second strap tying assembly. Each finger assembly includes a lock which grips a corresponding end of the baling strap. The first and second strap tying assemblies operatively rotate around a compressed bale so as to direct the baling strap circumferentially around the bale. The strap tying assemblies and finger assemblies, in combination, articulating to bring the opposite ends of the baling strap into overlying relationship with one another, for friction welding, while the press is still forming the bale.
In one aspect of the invention, the first and second strap tying and finger assemblies operatively rotate in a downward direction so as to bring the opposite ends of the baling strap into overlying relationship with one another for welding in a region corresponding to the bottom of the formed bale. In another aspect of the invention the first and second strap tying and finger assemblies operatively rotate in an upward direction so as to bring the opposite ends of the baling strap into overlying relationship with one another for welding in a region corresponding to the top of the formed bale.
In a further aspect of the invention, a multiplicity of first and second strap tying assemblies are mounted in spaced-apart fashion along a mounting beam. The multiplicity of first and second strap tying assemblies simultaneously operating so as to tie a multiplicity of baling straps around a bale in a single operation.